CN1937602A - Method and device for broadening multi-carrier communication coherent bandwidth - Google Patents

Abstract

The invention advances a method device for broadening multiple carrier communication coherence bandwidth by cyclic shift of sampled value of time-domain signal in accordance with OFDM system. In OFDM system, it makes cyclic shift on received time-domain data sequence without cyclic prefix. And it comprises: deleting data segment A from OFDM symbol without cyclic prefix and simultaneously adding the data segment to the tail of the OFDM symbol; therefore, signal distortion caused by channel can be corrected by frequency-domain single tapping equilibrium. And it is simple to implement, able to act as an independent module applied to any frequency-domain pilot-based OFDM and MIMO-OFDM system channel estimation so as to improve system performance.

Description

A kind of method of broadening multi-carrier communication coherent bandwidth and device thereof

Technical field

The invention belongs to the communications field, relate to multi-carrier transmission, especially orthogonal frequency division multiplex OFDM (Othogonal Frequency Division Multiplexing) technology.

Background technology

The aerial signal transmission technology has become new research focus.In order to obtain spectrum efficiency up to 10bps/Hz, support the communication requirement of several scenes, support various adaptive control technologies, the signal transmission technology of new mobile communication system must be supported more any similar technology more performance than in the past, keeps controllable implementation complexity simultaneously.In wide-band mobile communication system, because the influence of multipath, the signal that causes transmitting suffers frequency selective fading.Orthogonal frequency division multiplex OFDM (Othogonal Frequency DivisionMultiplexing) technology (be called for short OFDM technology) is with the ability of its born anti-channel multi-path, becomes one of the core technology of the signal transmission of the 4th third-generation mobile communication just day by day.Ofdm system is divided into a large amount of arrowbands flat fading subchannel by discrete Fourier transform (DFT) DFT with a wideband frequency Selective Fading Channel.In order to remedy the influence of each subchannel decline, ofdm system must adopt estimated channel that each subchannel demodulated symbols is carried out single tap equalization.Therefore, channel estimated accuracy directly influences the performance of balanced back symbol judgement.In ofdm system, channel estimation methods commonly used can be divided into two classes [document 1:Classen, F.andSpeth, M.and Meyr, H. " Channel Estimation Units for an OFDM Systemsuitable for Mobile Communications " .In Mobilecommunication:ITG-Fachbericht, Munchen, ITG, VDE-Verlag, BerlinOffenbach, 1995.].One class is based on the decision-directed DD method of judgement data, be also referred to as blind estimating method [document 2:Muquet B., Courville M., Duhamel P., " Subspace-based blindand semi-blind channel estimation for OFDM systems; " IEEE Transactionson Signal Processing, 2002, Vol.50 (7), pp.1699-1712. document 3:Stefan A.Fechtel and Heinrich Meyr. " Optimal parametric feedforward estimationof frequency selective fading radio channels " IEEE Transaction onCommunication, 1994, Vol.42 (2/3/4), pp.1639-1650.]; Blind estimating method does not need to send any auxiliary data, so system spectrum utilance height.But it need utilize the court verdict of data.If adjudicate wrongly, cause error propagation easily.Simultaneously, blind algorithm for estimating need utilize lot of data, therefrom extracts channel statistic property, could obtain one and estimate reliably, thereby limit the application of this algorithm under the fast time variant channel.Another kind of auxiliary PSA method [the document 4:J.van de Beek of pilot tone that is based on pilot tone, training symbol or training sequence, Edfors O, Sandell M., etc. " On channelestimation in OFDM systems, " IEEE Vehicular Technology Conference, Chicago, IL, 1995, Vol.2, pp.815-819.; Document 5:Li Y., " Pilot-symbol-aidedchannel estimation for OFDM in wireless systems, " IEEE Transaction onVehicular Technology, 2000, Vol.49 (4), pp.1207-1215.; Document 6:MorelliM.and Mengali U. " A Comparison of Pilot-Aided Channel EstimationMethods for OFDM Systems " IEEE Transaction on Signal Processing, 2001,49 (12), pp.3065-3073.; Document 7:Negi R., Cioffi J., " Pilot tone selectionfor channel estimation in a mobile OFDM system; " IEEE Transaction onConsumer Electronics, 1998, Vol.44 (3), pp.1122-1128.; Document 8:Rinne J.and Renfors M. " Pilot spacing in orthogonal frequency divisionmultiplexing systems on practical channels; " IEEE Transaction ConsumerElectronics, 1996, Vol.42 (4), pp.959-962.; Document 9:Yeh C.S and Lin Y.and Wu Y., " OFDM System Channel Estimation Using Time-Domain TrainingSequence for Mobile Reception of Digital Terrestrial Broadcasting; " IEEE Transactions on Broadcasting, 2000, Vol.46 (3), pp.215-220.; Document 10:Mignone V., Morello A., " CD3-OFDM:A novel demodulation schemefor fixed and mobile receivers ", IEEE Transaction on Communication, 1996, Vol.44 (9), pp.1144-1151.].Pilot tone inserted mode commonly used generally is divided into two kinds of packet-type block-type and comb type comb-type.Adopting the channel estimation methods of station work sequence is every several OFDM symbols, takes out whole subchannel transmission pilot tones of a symbol, and the subchannel data of other symbol is estimated to obtain [document 6, document 8] by time domain interpolation or decision feedback algorithms.Adopt comb type pilot tone to estimate channel [document 5; Document 11:Hsieh M H; Wei C H. " Channel estimation for OFDM systembased on comb-type pilot arrangement in frequency selective fadingchannels; " IEEE Transactions on Consumer Electronics, 1998,44 (1), 217-225.].Subchannel data promptly in each OFDM symbol, distributes experimental process Channel Transmission pilot tone, in case after pilot subchannel estimated, can obtain by interpolation.When so this pilot frequency mode is fit in a disguised form to fading channel faster.

Pilot tone the time, the insertion of bidimensional frequently is subjected to the restriction of channel coherence time and coherence bandwidth at interval.Promptly be less than at interval in the insertion of time domain the coherence time of channel, and be less than the coherence bandwidth of channel at the interval of frequency domain.If the channel estimating interpolation algorithm adopts simple first-order linear interpolation or Lagrangian second order interpolation, then the insertion of pilot tone at interval also should be littler.For the bigger ofdm communication system of coverage, the channel delay expansion is particularly serious to the influence of interpolation channel estimating performance.Be to guarantee precision of channel estimation, the method that adopts is to increase number of pilots reducing the interval of pilot tone usually, but so can reduce the availability of frequency spectrum of system.

Existing ofdm system based on the pilot tone channel estimating is under the condition that guarantees channel estimating performance, or by increasing number of pilots, to reduce the complexity of channel estimating; Adopt Wiener filtering algorithm for estimating based on least mean-square error.The former will reduce the availability of frequency spectrum of system, and the latter will improve the implementation complexity of system.

Summary of the invention

The method and the device thereof that the purpose of this invention is to provide a kind of broadening multi-carrier communication coherent bandwidth by expanding the channel coherence bandwidth, improve channel estimating performance.

For achieving the above object, solution of the present invention is: propose a kind of method and implement device thereof by time-domain signal sampled value cyclic shift broadening multi-carrier communication coherent bandwidth.In ofdm system, if the bandwidth of each subcarrier much smaller than the coherence bandwidth of channel, then the channel of each subcarrier correspondence can be thought flat fading, this moment, system only need adopt the frequency domain list tap equalization to get final product compensate for channel distortions.Channel estimating plays crucial effects to the bit of ofdm system and power division and input.Ofdm system adopts the channel estimation methods based on pilot tone usually.Pilot tone is subjected to the restriction of channel coherence bandwidth at interval in the insertion of frequency domain.When the frequency domain interval of pilot tone during near the coherence bandwidth of channel, the estimated performance of the subchannel data that will severe exacerbation obtains by linear interpolation.The coherence bandwidth of channel depends on the time delay expansion of channel, that is the impulse response of channel distributes.Because the time, the symmetry of bidimensional frequently, channel impulse response can be regarded as the spectrum of channel frequency response.When the accurate timing of OFDM receiver synchronous, i.e. fast fourier transform FFT window original position first sampled value place after removing Cyclic Prefix, the spectrum and the channel impulse response of the channel frequency response correspondence that the OFDM data after demodulating is experienced are identical.Like this, article one path of channel can be regarded as the DC component of channel frequency response, and that paths can be considered higher harmonic wave component at last, and the expansion of the time delay of whole channel can be considered " bandwidth " of channel frequency response.Have symmetry because spectrum distributes, promptly in the scope of a fft block length, two ends are low frequency component, and the centre is a high fdrequency component.Obviously,, can reduce " bandwidth " of the corresponding spectrum of channel frequency response, thereby correspondingly expand the coherence bandwidth of channel frequency response if with above-mentioned channel impulse response cyclic shift left.Above-mentioned cyclic shift can be finished by the time domain receiving data sequence behind the removal Cyclic Prefix is carried out cyclic shift.When received signal is correct regularly synchronously, promptly fast fourier transform FFT window original position is within Cyclic Prefix, and the FFT window data block of taking out does not have the influence of intersymbol interference.To several sampled values of data block ring shift left that the FFT window takes out, carry out the FFT conversion then.Algorithm for estimating such as least square LS or minimal linear mean square error LMMSE can be adopted at frequency domain to pilot subchannel, the linear interpolation algorithm for estimating can be adopted the data subchannel.The sampled value number of cyclic shift depends on the channel power time delay distribution.This number promptly can fixedly provide by empirical value according to the time delay expansion of channel, also can provide in real time by timing error.

This programme is realized simple, can be used as an independently module, is applied among any OFDM and multiple-input and multiple-output MIMO-OFDM system channel estimation scheme based on pilot tone, to improve systematic function.

A kind of method of broadening multi-carrier communication coherent bandwidth is carried out cyclic shift to the time domain receiving data sequence behind the removal Cyclic Prefix.

Further, the cyclic shift amount is data segment A, specifically comprises: data segment A is deleted from remove the Cyclic Prefix in OFDM System symbol, simultaneously this segment data is added to the afterbody of OFDM symbol; Therefore the distorted signals that is caused by channel can be proofreaied and correct by for example frequency domain list tap equalization.

If channel is two footpath fading channels, its impulse response can be expressed as:

h(n)＝αδ(n)+βδ(n-τ) (1)

Wherein, α and β are respectively the complex gain of channel two paths, and τ is the time delay in second path; Suppose that the accurate timing of OFDM receiver is synchronous, i.e. fast fourier transform FFT window original position first sampled value place after removing Cyclic Prefix; At this moment, channel frequency response is

$H\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}h\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;kn}/N}$

＝α+βe ^-j2πkτ/N，k＝0，...，N-1 (2)

Wherein, N is that OFDM modulation FFT conversion is counted;

If α=β, channel frequency response becomes:

H(k)＝α(1+e ^-j2πkτ/N)，k＝0，…，N-1 (3)

The FFT transform block that accurate synchronously back is taken out ξ the sampled value that circulate left, (ξ sampled value removed before also being about in the FFT transform block, and this ξ sampled value is added to the afterbody of FFT transform block), then the channel frequency response that experienced of OFDM data after demodulating becomes:

H(k)＝α(1+e ^-j2πkτ/N)e ^j2πkξ/N，k＝0，…，N-1 (4)

If cyclic shift amount ξ=τ/2, then channel frequency response becomes

H(k)＝α(e ^jπkτ/N+e ^-jπkτ/N)，k＝0，…，N-1 (5)

＝2αcos(πkτ/N)

Under the multidiameter fading channel of reality,, provide the root mean square time delay expansion that statistics optimum cycle displacement is a channel according to the time delay expansion of channel; Or at each channel impulse response constantly, real-time optimization cyclic shift amount is promptly determined the channel delay expansion according to previous moment estimated channel impulse response, is used for the cyclic shift amount of current time.

Channel root mean square time delay expanded definition is:

${\mathrm{\&tau;}}_{\mathrm{rms}}={\left[\frac{{\&Integral;}_{-\&infin;}^{\&infin;}{(\mathrm{\&tau;}-\stackrel{\&OverBar;}{\mathrm{\&tau;}})}^{2}P\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}{{\&Integral;}_{-\&infin;}^{\&infin;}P\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}\right]}^{1/2}={\left[\frac{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2{({\mathrm{\&tau;}}_l-\stackrel{\&OverBar;}{\mathrm{\&tau;}})}^2}{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2}\right]}^{1/2}---\left(6\right)$

In the formula

$\stackrel{\&OverBar;}{\mathrm{\&tau;}}=\frac{{\&Integral;}_{-\&infin;}^{\&infin;}P\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}{{\&Integral;}_{-\&infin;}^{\&infin;}\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}=\frac{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">l</figure-callout>}}^2{\mathrm{\&tau;}}_l}{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2}---\left(7\right)$

P (τ) can be expressed as for power time delay distributes

$P\left(\mathrm{\&tau;}\right)=E\left\{{\left|h(\mathrm{\&tau;},t)\right|}^2\right\}=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">l</figure-callout>}}^2\mathrm{\&delta;}(\mathrm{\&tau;}-{\mathrm{\&tau;}}_l)---\left(8\right)$

In the formula

$h(\mathrm{\&tau;},t)=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l\left(t\right)\mathrm{\&delta;}(\mathrm{\&tau;}-{\mathrm{\&tau;}}_l)---\left(9\right)$

Be the multiple impulse response of time-variant multipath channel, τ _lBe the time delay of l paths, h _l(t) be the t complex gain of l paths constantly, ${\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">l</figure-callout>}}^2=E\&lsqb;{\left|h_l\left(t\right)\right|}^2\&rsqb;,$ The average power of representing the l paths;

Corresponding given mobile communication application scene, by Channel Modeling, the channel power time delay distribution P (τ) of available acquisition experience, that is know that the channel path of experience counts the average power α in L, path _l ²With τ in relative time delay _l, can determine channel root mean square time delay extended by tau by (6) _Rms, sampling interval normalization is used in the expansion of this channel root mean square time delay, get final product the cyclic shift amount.

Channel impulse response with instantaneous estimation replaces the power time delay in the described method to distribute, and determines the channel delay expansion, adopts identical method, obtains the cyclic shift amount.

A kind of method of broadening multi-carrier communication coherent bandwidth is to realize by the frequency domain data after the OFDM demodulation be multiply by phase rotation coefficient.

By H (k)=α (1+e ^{-j2 π k τ/N}) e ^{J2 π k ξ/N}, k=0 ..., N-1 as can be known, the FFT transform block that accurate synchronously back is taken out ξ the sampled value that circulate left, equivalence is that the data of k subcarrier after the OFDM demodulation multiply by phase rotation coefficient e ^{J2 π k ξ/N}

A kind of device of broadening multi-carrier communication coherent bandwidth, it has the structure that realizes said method.

Owing to adopted such scheme, the present invention has the following advantages:

The present invention has widened the coherence bandwidth of channel, thereby under the condition that adopts the same pilot number, can improve the channel estimating performance of system by simple regularly cyclic shift.Perhaps, under identical channel estimating performance condition, can increase pilot interval, reduce number of pilots, thereby improve the system spectrum utilization ratio.

This programme is realized simple, can be used as an independently module, is applied in any ofdm system channel estimation scheme based on pilot tone, especially in the channel estimation method based on the ofdm system of multiple-input and multiple-output (MIMO).Because mimo system often needs to estimate a plurality of channels simultaneously, so the availability of frequency spectrum of pilot tone is most important.When number of transmit antennas was big, because the restriction of channel coherence bandwidth, pilot interval can not be too big, for guaranteeing channel estimating performance, must increase number of pilots, thereby reduce the system spectrum utilance.After adopting this programme, system's coherence bandwidth is widened, and can improve the channel estimating performance that receiver adopts simple plug wire value-based algorithm under the situation that does not increase number of pilots.

Description of drawings

Fig. 1 is a channel estimation methods schematic diagram of the present invention;

Fig. 2 is under the two footpath channels, regularly the real part and the imaginary part schematic diagram of channel frequency response before and after the cyclic shift;

Fig. 3 is the real part and the imaginary part schematic diagram of timing cyclic shift front and back channel frequency response under the SUI-4 channel;

Fig. 4 estimates the mean square error schematic diagram under the SUI-4 channel;

Fig. 5 is a bit error code performance schematic diagram under the SUI-4 channel.

Embodiment

Specifically see also and see Fig. 1, suppose the length of the maximum delay expansion of multipath channel, by the time domain receiving data sequence behind the removal Cyclic Prefix is carried out cyclic shift less than Cyclic Prefix (CP).Specifically as shown in Figure 1, data segment A is deleted from remove the Cyclic Prefix in OFDM System symbol, simultaneously this segment data is added to the afterbody of OFDM symbol.Obviously, the circular convolution characteristic in the received signal is still kept, and therefore the distorted signals that is caused by channel still can be proofreaied and correct by frequency domain list tap equalization.

By the data segment cyclic shift of the OFDM symbol middle front part after the timing synchronously being arrived the afterbody of OFDM symbol, can expand the coherence bandwidth of channel, prove as follows.

Be reduced representation, suppose that channel is two footpath fading channels, its impulse response can be expressed as:

h(n)＝αδ(n)+βδ(n-τ) (1)

Wherein, α and β are respectively the complex gain of channel two paths, and τ is the time delay in second path.

Suppose that the accurate timing of OFDM receiver is synchronous, i.e. fast fourier transform FFT window original position first sampled value place after removing Cyclic Prefix.At this moment, channel frequency response is

$H\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}h\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;kn}/N}$

＝α+βe ^-j2πkτ/N，K＝0，…，N-1(2)

Wherein, N is that OFDM modulation FFT conversion is counted.

If α=β, (channel frequency response becomes:

H(k)＝α(1+e ^-j2πkτ/N)，k＝0，…，N-1 (3)

Obviously, the coherence bandwidth of channel and 2 π τ/N are inversely proportional to.If the accurate synchronously FFT transform block that takes out of back ξ the sampled value that circulate left, then the channel frequency response that experienced of OFDM data after demodulating becomes:

H(k)＝α(1+e ^-j2πkτ/N)e ^j2πkξ/N，k＝0，…，N-1 (4)

If, cyclic shift amount ξ=τ/2, then channel frequency response becomes

H(k)＝α(e ^jπkτ/N+e ^-jπkτ/N)，k＝0，…，N-1 (5)

＝2αcos(πkτ/N)

Obviously, the coherence bandwidth and the π τ/N of channel are inversely proportional at this moment.Promptly do not compare with there being regularly the channel frequency response of cyclic shift, the channel coherence bandwidth has increased by one times.

Just for the coherence bandwidth that adopts cyclic shift can expand channel is described, the hypothesis that is adopted is an extreme case to this part content, just for simplifying the analysis.Under prevailing situation,, can obtain same conclusions by similar derivation.This conclusion can be proved by emulation.

If receiver does not have accurate timing synchronous, promptly there is timing error, then there are two kinds of situations: first kind of situation, receiver is incorrect synchronously, be that fast fourier transform FFT window original position is outside Cyclic Prefix, this moment, corresponding any OFDM receiver all can produce intersymbol interference, and therefore corresponding any OFDM receiver all will be avoided; Second kind of situation, the receiver accurate synchronization, promptly fast fourier transform FFT window original position is equivalent to the received signal ring shift right this moment within Cyclic Prefix.Because the algorithm that proposes is a ring shift left, when internal circulating load is enough big, obviously can offset the influence of timing error.

Under the multidiameter fading channel of reality, because the distribution of multipath is at random, can provide the root mean square time delay expansion that statistics optimum cycle displacement is a channel this moment according to the time delay expansion of channel.Owing to have bigger variation at difference channel impulse response constantly, if at each channel impulse response constantly, real-time optimization cyclic shift amount, promptly according to previous moment estimated channel impulse response calculating channel time delay expansion, the cyclic shift amount that is used for current time then can further improve systematic function.

Below specify method according to the definite cyclic shift amount of channel delay expansion.

Channel root mean square time delay expanded definition is:

${\mathrm{\&tau;}}_{\mathrm{rms}}={\left[\frac{{\&Integral;}_{-\&infin;}^{\&infin;}{(\mathrm{\&tau;}-\stackrel{\&OverBar;}{\mathrm{\&tau;}})}^{2}P\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}{{\&Integral;}_{-\&infin;}^{\&infin;}P\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}\right]}^{1/2}={\left[\frac{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2{({\mathrm{\&tau;}}_l-\stackrel{\&OverBar;}{\mathrm{\&tau;}})}^2}{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2}\right]}^{1/2}---\left(6\right)$

In the formula

$\stackrel{\&OverBar;}{\mathrm{\&tau;}}=\frac{{\&Integral;}_{-\&infin;}^{\&infin;}\mathrm{\&tau;P}\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}{{\&Integral;}_{-\&infin;}^{\&infin;}P\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}=\frac{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">l</figure-callout>}}^2{\mathrm{\&tau;}}_l}{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2}---\left(7\right)$

P (τ) can be expressed as for power time delay distributes

$P\left(\mathrm{\&tau;}\right)=E\left\{{\left|h(\mathrm{\&tau;},t)\right|}^2\right\}=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">l</figure-callout>}}^2\mathrm{\&delta;}(\mathrm{\&tau;}-{\mathrm{\&tau;}}_l)---\left(8\right)$

In the formula

$h(\mathrm{\&tau;},t)=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l\left(t\right)\mathrm{\&delta;}(\mathrm{\&tau;}-{\mathrm{\&tau;}}_l)---\left(9\right)$

Be the multiple impulse response of time-variant multipath channel, τ _lBe the time delay of l paths, h _l(t) be the t complex gain of l paths constantly. ${\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A20051002991400181.png"\; state="\{\{state\}\}">l</figure-callout>}}^2=E\&lsqb;{\left|h_l\left(t\right)\right|}^2\&rsqb;,$ The average power of representing the l paths.

Corresponding given mobile communication application scene, by Channel Modeling, the channel power time delay distribution P (τ) of available acquisition experience, that is know that the channel path of experience counts the average power α in L, path _l ²With τ in relative time delay _lCan determine channel root mean square time delay extended by tau by (6) _RmsSampling interval normalization is used in the expansion of this channel root mean square time delay, get final product the cyclic shift amount.

If replace power time delay used in the said method to distribute the channel impulse response of instantaneous estimation, determine the channel delay expansion, adopt identical method, also can get the cyclic shift amount.

Another aspect by the frequency domain data after the OFDM demodulation be multiply by phase rotation coefficient, also can reach the effect identical with the time domain cyclic shift, yet this method will increase the computation complexity of system.

By (4) as can be known, the FFT transform block that accurate synchronously back is taken out ξ the sampled value that circulate left, equivalence is that the data of k subcarrier after the OFDM demodulation multiply by phase rotation coefficient e ^{J2 π k ξ/N}

Simulated environment 1:

Channel width: 10M, channel model: two footpath constant amplitude channels, time delay 0,1.5 μ s, multipath gain 0.4749-j*0.5765,0.4749-j*0.5765.

Simulation result as shown in Figure 2.

Fig. 2 has compared under the two footpath channels, 8 sampled values of timing cyclic shift, real part and the imaginary part of front and back channel frequency response CFR.As seen from the figure, the channel after the cyclic shift (Shifted CFR) coherence bandwidth has increased by one times than original channel (Real CFR) is approximate.

Simulated environment 2:

Channel width: 7MHz; Systematic sampling frequency 8MHz; Channel model a: sample of SUI-4 channel, multidiameter delay 0,1.5,4.0 μ s, multipath gain 0.4749-j*0.5765,0.2183+j*0.0469 ,-0.1181-j*0.2249.

Simulation result as shown in Figure 3.

Fig. 3 has compared SUI-4 channel real part and the imaginary part of 10 sampled values front and back of timing cyclic shift channel frequency response CFR down.As seen from the figure, after the cyclic shift, the real part of channel frequency response and the variation tendency of imaginary part are obviously slowed down.

Simulated environment 3:

Channel width: 7MHz; Systematic sampling frequency 8MHz; Channel model: SUI-4, multidiameter delay 0,1.5,4.0 μ s, multipath average power 0 ,-4 ,-8dB, the root mean square time delay is expanded 1.257 μ s; Chnnel coding: convolution code adds the RS sign indicating number.Convolution code constraint length 7, generator polynomial [171,133], decoding: 8 grades of 3bit quantize Viterbi soft decoding, decoding depth 34.The modulating-coding pattern is as shown in table 1.

Table 1 is adjusted coding mode

Modulation system	Total bitrate	The RS sign indicating number	The convolution code code check
				BPSK
	1/2	(12，12，0)	1/2
				QPSK	1/2	(32，24，4)	2/3
16-QAM	1/2	(64，48，8)	2/3

Channel estimation method: pilot subchannel adopts least square LS to estimate, subchannel data adopts Lagrangian second order interpolation to estimate.

Equalization algorithm: ZF ZF equilibrium.

Simulation result such as Fig. 4,5, Figure 4 and 5 have compared regularly 10 sampled values front and back channel estimating mean square errors of cyclic shift and bit error code performance respectively under the SUI-4 channel.As seen from the figure, when signal to noise ratio is higher, adopt regularly the MSER of the channel estimation method of cyclic shift not have the algorithm for estimating of regularly displacement that obvious reduction is arranged, and the bit error code performance also is significantly improved.Improve particularly evident for the systematic bits error rate that adopts high order modulation.

Claims (11)

1, a kind of method of broadening multi-carrier communication coherent bandwidth is characterized in that: the time domain receiving data sequence behind the removal Cyclic Prefix is carried out cyclic shift.

2, the method for broadening multi-carrier communication coherent bandwidth according to claim 1 is characterized in that:

The cyclic shift amount is data segment A, specifically comprises: data segment A is deleted from remove the Cyclic Prefix in OFDM System symbol, simultaneously this segment data is added to the afterbody of OFDM symbol.

3, the method for broadening multi-carrier communication coherent bandwidth according to claim 2 is characterized in that: can be proofreaied and correct by frequency domain list tap equalization by the distorted signals that channel causes.

4, the method for broadening multi-carrier communication coherent bandwidth according to claim 1 is characterized in that: establishing channel is two footpath fading channels, and its impulse response can be expressed as:

h(n)＝αδ(n)+βδ(n-τ) (1)

Wherein, α and β are respectively the complex gain of channel two paths, and τ is the time delay in second path;

Suppose that the accurate timing of OFDM receiver is synchronous, i.e. fast fourier transform FFT window original position first sampled value place after removing Cyclic Prefix; At this moment, channel frequency response is

$\begin{array}{ccc}& H\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}h\left(n\right)e^{-j2\mathrm{\&pi;kn}/N}& \\ & =\mathrm{\&alpha;}+\mathrm{\&beta;}{e}^{-j2\mathrm{\&pi;k\&tau;}/N},& k=0,...,N-1---\left(2\right)\end{array}$

Wherein, N is that OFDM modulation FFT conversion is counted;

If α=β, channel frequency response becomes:

H(k)＝α(1+e ^-j2πkτ/N)，k＝0，…，N-1 (3)

The FFT transform block that accurate synchronously back is taken out ξ the sampled value that circulate left, ξ sampled value removed before also being about in the FFT transform block, and add this ξ sampled value the afterbody of FFT transform block to, then the channel frequency response that experienced of OFDM data after demodulating becomes:

H (k)=α (1+e ^{-j2 π k τ/N}) e ^{J2 π k ξ/N}, k=0 ..., N-1 (4) establishes cyclic shift amount ξ=τ/2, and then channel frequency response becomes

H(k)＝α(e ^jπkτ/N+e ^-jπkτ/N)，k＝0，…，N-1 (5)

＝2αcos(πkτ/N)

5, the method for broadening multi-carrier communication coherent bandwidth according to claim 1 and 2 is characterized in that: under the multidiameter fading channel of reality, according to the time delay expansion of channel, provide the root mean square time delay expansion that statistics optimum cycle displacement is a channel.

6, the method for broadening multi-carrier communication coherent bandwidth according to claim 1 and 2, it is characterized in that: at each channel impulse response constantly, real-time optimization cyclic shift amount, promptly determine the channel delay expansion, be used for the cyclic shift amount of current time according to previous moment estimated channel impulse response.

7, according to the method for claim 5 or 6 described broadening multi-carrier communication coherent bandwidths, it is characterized in that: channel root mean square time delay expanded definition is:

${\mathrm{\&tau;}}_{\mathrm{\&rho;\&mu;\&sigma;}}={\&lsqb;\frac{{\&Integral;}_{-\&infin;}^{\&infin;}{(\mathrm{\&tau;}-\stackrel{\&OverBar;}{\mathrm{\&tau;}})}^2\mathrm{\&pi;}\left(\mathrm{\&tau;}\right)\mathrm{\&delta;\&tau;}}{{\&Integral;}_{-\&infin;}^{\&infin;}\mathrm{\&pi;}\left(\mathrm{\&tau;}\right)\mathrm{\&delta;\&tau;}}\&rsqb;}^{1/2}={\&lsqb;\frac{\underset{\mathrm{\&lambda;}=0}{\overset{\mathrm{\&Lambda;}-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_{\mathrm{\&lambda;}}^2{({\mathrm{\&tau;}}_{\mathrm{\&lambda;}}-\stackrel{\&OverBar;}{\mathrm{\&tau;}})}^2}{\underset{\mathrm{\&lambda;}=0}{\overset{\mathrm{\&Lambda;}-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_{\mathrm{\&lambda;}}^2}\&rsqb;}^{1/2}---\left(6\right)$

In the formula

$\stackrel{\&OverBar;}{\mathrm{\&tau;}}=\frac{{\&Integral;}_{-\&infin;}^{\&infin;}\mathrm{\&tau;p}\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}{{\&Integral;}_{-\&infin;}^{\&infin;}p\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}}=\frac{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2{\mathrm{\&tau;}}_l}{\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}_l^2}---\left(7\right)$

P (τ) can be expressed as for power time delay distributes

$P\left(\mathrm{\&tau;}\right)=E\left\{\right|h(\mathrm{\&tau;},t){|}^2\}=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_l^2\mathrm{\&delta;}(\mathrm{\&tau;}-{\mathrm{\&tau;}}_1)---\left(8\right)$

In the formula

$h(\mathrm{\&tau;},t)=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l\left(t\right)\mathrm{\&delta;}(\mathrm{\&tau;}-{\mathrm{\&tau;}}_l)---\left(9\right)$

Be the multiple impulse response of time-variant multipath channel, τ _lBe the time delay of l paths, h _l(t) be the t complex gain of l paths constantly, ${\mathrm{\&alpha;}}_l^2=E\&lsqb;|h_l\left(t\right){|}^2\&rsqb;,$ The average power of representing the l paths;

Corresponding given mobile communication application scene, by Channel Modeling, the channel power time delay distribution family P (τ) of available acquisition experience, that is know that the channel path of experience counts the average power α in L, path _l ²With τ in relative time delay _l, can determine channel root mean square time delay extended by tau by (6) _Rms, sampling interval normalization is used in the expansion of this channel root mean square time delay, get final product the cyclic shift amount.

8, the method for broadening multi-carrier communication coherent bandwidth according to claim 7 is characterized in that:

Channel impulse response with instantaneous estimation replaces the power time delay in the described method to distribute, and determines the channel delay expansion, adopts identical method, obtains the cyclic shift amount.

9, a kind of method of broadening multi-carrier communication coherent bandwidth is characterized in that: be to realize by the frequency domain data after the OFDM demodulation be multiply by phase rotation coefficient.

10, the method for broadening multi-carrier communication coherent bandwidth according to claim 9 is characterized in that: by H (k)=α (1+e ^{-j2 π k τ/N}) e ^{J2 π k ξ/N}, k=0 ..., N-1 as can be known, the FFT transform block that accurate synchronously back is taken out ξ the sampled value that circulate left, equivalence is that the data of k subcarrier after the OFDM demodulation multiply by phase rotation coefficient e ^{J2 π k ξ/N}

11, a kind of device of broadening multi-carrier communication coherent bandwidth is characterized in that: it has the structure that realizes arbitrary described method among the claim 1-10.

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